UPSTREAM: firmware: arm_ffa: Add initial FFA bus support for device enumeration

The Arm FF for Armv8-A specification has concept of endpoints or
partitions. In the Normal world, a partition could be a VM when
the Virtualization extension is enabled or the kernel itself.

In order to handle multiple partitions, we can create a FFA device for
each such partition on a dedicated FFA bus. Similarly, different drivers
requiring FFA transport can be registered on the same bus. We can match
the device and drivers using UUID. This is mostly for the in-kernel
users with FFA drivers.

Link: https://lore.kernel.org/r/20210521151033.181846-2-sudeep.holla@arm.com


Tested-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
(cherry picked from commit e7818584)
Change-Id: I9a3ca8b3d254ecdf0dd3ca45ef87d1be08084b89
Bug: 168585974
Signed-off-by: Will Deacon <willdeacon@google.com>